The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Methods of automatic speed control are becoming more complex as features and capabilities are being added to vehicles and desired by customers. The most basic automatic speed control is conventional cruise control (CCC), which allows an operator to set a reference velocity and controls powertrain output to the reference velocity. Examples of more advanced versions becoming more popular are adaptive cruise control, speed limit following, and curve speed control.
Adaptive cruise control (ACC) is a control method for automatically controlling a vehicle within a lane of traffic, maintaining a desired velocity while maintaining a safe distance, or headway, from other vehicles in the same lane of travel. The essential function of ACC is target vehicle following which means that a host vehicle follows a target vehicle while maintaining a certain separation (e.g. time or distance) while attempting to maintain the desired velocity. The host vehicle is the vehicle being controlled by ACC, and the target vehicle is the vehicle in front of the host vehicle.
Speed limit following (SLF) is a method of vehicular velocity control, wherein a vehicle subsystem monitors a current speed limit for a road currently being traveled upon and the speed limit for the road at a distance in front of the vehicle. The vehicle velocity is maintained in relation to the monitored speed limit(s). At steady state, the vehicle is operated similarly to a vehicle with CCC, with the reference velocity for the vehicle set to the speed limit. In transitions, one exemplary method is reacting to pending changes in speed limits which includes reducing reference velocity before the approach of a lower speed limit zone and raising the reference velocity after a higher speed limit zone is entered. In this preferred method, the speed limit is never violated. Vehicular velocity is maintained at or below the speed limit, including transitional increases and decreases in vehicle velocity. Speed limits for the road currently being traveled upon and for the road in front of the vehicle can be determined in a number of ways. One preferred method includes coordinated use of a global positioning device (GPS) and a digital map database, including speed limit data for an identified stretch of road and data describing points of speed limit change on a road.
Curve speed control (CSC) is a method of vehicular velocity control wherein a vehicle subsystem monitors a current road curvature and a road curvature some distance ahead. Safe velocities on a straight road being traveled upon and safe velocity on a similar but curved road can be different. Force on a vehicle caused by angular acceleration through a curve is a destabilizing factor on the vehicle not present on a straight stretch of road. Force on the vehicle caused by angular acceleration through a given curve can be reduced by decreasing vehicle velocity. Curve speed control monitors the curvature of the road currently being traveled upon and the curvature of road in front of the vehicle while vehicle velocity is reduced based upon predicted effects of angular acceleration upon the vehicle. Speed limit data for a particular road and curvature data for a stretch of road can be determined in a number of ways. For example, a GPS device and a digital map database can be utilized to look-up or determine both speed limits and road curvature. Additionally or alternatively, a camera or visual imaging device can be utilized in combination with image recognition programming to estimate road curvature for the road being traveled upon.
The above described speed control devices can act together to control the vehicle through a single vehicle speed control system, for example, a throttle control and a brake control. Such a combination of speed control methods can be accomplished, for example, in a multiple feature cruise control, monitoring as inputs velocity and/or acceleration commands from modules performing one of the aforementioned speed control methods and prioritizing a single set of commands to the vehicle speed control system.
Travel in a lane of traffic is inherently a variable and complicated situation. A method to smoothly control velocity of a vehicle based upon an integration of conventional cruise control, adaptive cruise control, speed limit following control, and curve speed control would be beneficial to the operation of the vehicle and occupant comfort.